1. Field of the Invention
The present invention relates to a power assist bicycle in which a power unit accommodated with an electric motor is mounted to a bicycle body so that the power assist bicycle can easily run along an upward slope or against a head wind with an assisted pedal leg-power by the assistance of drive power outputted from the electric motor.
2. Description of the Related Art
For a power assist bicycle of this kind, it is necessary to mount a battery unit as a power source to a bicycle body together with a power unit. In such a structure, however, according to the mounting position of the battery unit generally having a large weight, the center of gravity of the bicycle body may be made high or the mass of the body (positions of the heavy parts) may be dispersed, which may result in that a steering stability of the bicycle is made worse or easy conveyance thereof is made worse. For this reason, it will be better in design to arrange the battery unit in the vicinity of the power unit.
In conventional arrangements of the battery unit of a power assist bicycle, the battery unit is arranged, in the vicinity of the power unit, along an upper edge of a main pipe (i.e., a big pipe extending obliquely rearward in a downward direction from a head pipe) of a bicycle body frame or along a rear edge of a saddle (seat) pipe.
Such arrangements, however, have created a number of problems or disadvantages.
In an arrangement where the battery unit is disposed along the upper edge of the main pipe, the battery unit is positioned at a portion in the front side of a V-shaped leg space (i.e., a space through which a leg of a rider moves when getting on or off the bicycle (saddle) formed between the main pipe and the saddle pipe. According to this arrangement, when a rider rides on a saddle or gets off therefrom, it is necessary for the rider to ride over both the main pipe and the battery unit, thus being inconvenient.
In another arrangement, the battery unit is disposed along the rear edge of the saddle pipe. Although inconvenience caused in the above arrangement can be reduced, the structure near the rear wheel will be made complicated. In addition, the saddle obstructs the mounting structure of the battery unit. Moreover, the center of gravity of the bicycle is moved rearward, so that a stable steering stability cannot be accurately ensured, thereby providing additional problems or drawbacks in this arrangement.